The present invention relates to the bead portion of a pneumatic tire, and more specifically to a tire having a bead portion which has a pentagonal shape, no apex, a high turn-up and a locked-in structure when mounted on a specified rim.
The present invention is an improvement on U.S. Pat. No. 5,058,649 issued Oct. 22, 1991.
The desirability of having the turn-up portions of the carcass ply (or plies) of a pneumatic tire extend radially outwardly of the bead core the shortest possible distance is the premise on which prior art locked beads were developed. The proposed advantages included improved bead durability, and reduced material costs.
Referring to FIG. 3 there is shown a bead portion of a prior art tire as taught in commonly owned U.S. Pat. No. 4,922,985, issued May 8, 1990. The carcass ply 30 has a main portion that extends between both bead cores (not shown) of the tire and turn-up portions that are anchored around each bead core 31.
The "main portion of the carcass ply" is understood to mean the portion of the carcass ply which extends between the bead cores. It is understood that as used herein and in the claims a carcass ply comprises reinforcing cords embedded in an elastomeric substance and that these components are considered to be a single entity. Tires according to this prior art embodiment and U.S. Pat. No. 5,058,649 have the radially outer edges of the turn-up portions of the carcass ply disposed radially outwardly of the bead cores a minimal distance and are in contact with the main portion of the carcass ply. Suitable elastomeric materials surround the bead core, carcass ply, and other elastomeric components to complete the bead portion of the tire.
As used herein, the terms "radial" and "radially" refer to directions going towards or away from the axis of rotation of a tire. The terms "axial" and "axially" indicate directions that are parallel to the axis of rotation of a tire.
In tires according to this prior art embodiment and U.S. Pat. No. 5,058,649, a turn-up portion of the carcass ply 30 extends radially outwardly of the bead core 31 a minimal distance to allow for some pull-down of the carcass ply during the shaping and curing process. For example, in a passenger tire the edge of the turn-up portion may be located about 10 mm radially outwardly of the bead core.
In the prior art embodiment illustrated in FIG. 3, as well as in a tire and tire and wheel assembly according to U.S. Pat. No. 5,058,649, a clamping member 32 comprised a strip of side-by-side cords of a heat shrinkable material embedded in a suitable elastomeric substance having a permanent thermal shrinkage of at least 2%. This strip of cords extended circumferentially in contact with a radially innermost carcass ply 30 from a location radially and axially inward of the bead core 31 to a location radially outward of the bead core and adjacent to the main portion of the carcass ply, and there was no filler strip or apex disposed between the main portion and turn-up portion of the carcass ply. As used herein, a "cord" is understood to be either a single filament or a plurality of filaments twisted together with one another to form a cable.
The use of a single component for dual purposes as either a toe guard/clamping member or chafer/clamping member was believed to provide economical use of materials, labor, and machine time.
Other components that were located in the bead portion of some prior art tires included a toe guard and a chafer strip. Conventionally, a "toe guard" is a layer of reinforcing cords folded around the carcass ply and bead core on the side of the carcass ply furthest away from the bead core. The primary purpose of a toe guard is to protect the bead from damage during mounting of the tire on a rim and subsequent use of the tire on a vehicle. A chafer may be either a tough elastomeric material that protects the bead portion from abrasion during mounting and use of the tire, or a layer of fabric extending from radially inwardly of the bead core to the same radial height as the edge of the turn-up.
As used herein, "permanent thermal shrinkage" is understood to mean the intrinsic dimensional stability of a material when it is exposed to an elevated temperature as indicated by the percentage of permanent shrinkage. Generally, in the test procedure for shrinkage, a cord is exposed to a temperature of 177.degree. C., and its percentage of shrinkage is measured directly from a calibrated dial in a shrinkage meter, which determines the total shrinkage inherent in the material. Other tests for shrinkage are known to those skilled in the art.
Tires according to the prior art embodiment of FIG. 3 were manufactured using a clamping member in which the heat shrinkable material was 1260/2 Nylon 6,6, having a permanent thermal shrinkage of about 4%. A polyester or other heat shrinkable material having a permanent thermal shrinkage of at least 2% could also be employed in the practice of the prior art inventions. It is continually the goal in the art to simplify the construction and reduce the expense of building tires, yet improve the durability, handling, rolling resistance and other properties of tires.
Other objects of the invention will be apparent from the following description and claims.